Silverstag turned my companion intuition upside down, so I wrote out some notes to help me plan. Feel free to point out any errors or make recommendations.
** Other writer here, rewrote some stuff to improve on suggestions based on my experience with the game. Added my suggestions in Italics, tried to keep old suggestions. Removed some repetitive advice and moved it to the intro section. **
In Silverstag, each companion has three abilities, unlocked at levels 5, 12 and 20. Most companions have at least one ability that provides a bonus based on some combination of skills and/or attributes (most are based on just one skill). To get the best out of your companions, you should focus on the stats that benefit their abilities when you assign points at each new level. Check out the article on skills over at the general Mount&Blade wiki if you aren't familiar with what skills do, and which attributes govern them.
(Edited, but the point being made is intact) - Unless a companion is clearly combat-focused, they should be kept in the Foot Archer division and given a crossbow. This is because crossbows require only proficiency points to be used effectively, while (good) bows require investment in Power Draw, a STR skill, to be used at all. If there are extra skill points to be spent while leveling a companion, consider rounding general combat skills like Weapon master, Ironflesh, Shield, and Athletics to the companion's cap.
Or, consider giving your companions horses to improve your party's movement speed on the map. Most companions have at least 1 Riding, enough to ride a saddle horse, and can wield light lances. You could even get the best of both approaches if you equip your companions as crossbow or firearm users, put them on saddle horses, assign them to the archer division, and simply tell the whole division to dismount when you want to get them firing. The same could be done with cavalry archers, if you have too few to use them properly as a division.
MARNID (Likes Borscha, dislikes Alayen & Baheshtur)
Marnid is the best Quartermaster. His Cargomaster ability grants higher prices for items he sells based on his Persuasion skill, and increases the gold merchants have to barter with based on Trade. Level CHA for Persuasion, Trade, and Leadership, in that order. Read the INT book to round up to 12, and get AGI to 9 for a third Weapon Master point. Through Quick Study, he will gain extra experience based on INT, and can read books more quickly than most. Administrator provides various buffs when he's assigned as a Castle Steward or Captain of the Guard.
NIZAR (Likes Matheld, dislikes Alayen & Firentis)
Nizar is the best Gaoler, although this doesn't really kick in until level 12. He begins with decent combat skills that are beyond his stats, so don’t bother adding to STR and AGI. Level CHA for Prisoner Management, Persuasion, and Trade, and put any spare points into Leadership for the morale boost. Useful Contacts improves his abilities as a Gaoler, and also reduces chances of being discovered when sneaking into a town or castle.
KATRIN (Likes Bunduk, dislikes Firentis & Baheshtur)
Katrin is the best Storekeeper. She starts with an amazing 7 in Inventory Management which makes it easy to store vast amounts of food at a time, and her Chef ability increases the coverage of food by a static 25% with a morale bonus improvement based on her Trade skill. Level CHA for Trade, and also Leadership (For her Efficient ability, gives various buffs based on INT/Leadership when she's assigned as a castle steward). If you want to make full use of her Supply Runner ability, get AGl/Athletics up to 15/5, with extras going into Weapon Master. Rounding STR up is not needed since she starts with 3 Ironflesh already, unless it gets you a good piece of equipment.
ALAYEN (Noble; Likes Ymira, dislikes Nizar & Marnid)
Each of Alayen's three abilities draws upon three skills, under different attributes, so they can't all be put to their full use. The best ability to focus on is probably Tactician, because the required investment in the attribute/skill pair provides 5 leftover points instead of 2 for a similar combat value. Level INT/Tactics; the extra points can be used to make him a secondary Doctor or Scout, or to round up his combat skills/Leadership for his other abilities. Alternatively, you could build him simply as a AGL/Weapon Master/Riding light cavalry unit and ignore his two troop benefit abilities entirely, or level just CHA/Leadership for Commanding Presence. Alayen should always be given a weapon that deals cutting damage, to take advantage of Blademaster.
Baheshtur is fairly useful. Hunter is good, but not worth maxing INT for. I suggest rounding up to 12 to get Tracking to 4. You might consider making him your Tracker/Pathfinder/Spotter and really pumping INT, but I consider him too good of an archer for that, and there are weaker companions that can fill those roles. Focus on AGl/Weapon Master and either Riding/Horse Archery or Athletics and general combat skills, depending on whether you intend to use him as a light foot archer or a cavalry archer. As a cavalry archer, he can certainly do well, and you'll have to invest in AGl anyway, but he'll have an easier time receiving troop benefits from nearby allies as a foot archer. A good set of equipment for him would be a Khergit Bow, Lg. Bag of Khergit/Broadhead Arrows x2, and a 2h Sabre, whether on foot or on a horse.
Firentis is a decent fighter with no leadership or utility skills. His abilities lend themselves to a heavily armored Infantry unit, because a lower AGI will penalize Riding far more than Athletics. Level STR, prioritizing Ironflesh. Don’t neglect AGI entirely; the starting 12 is respectable early on, but eventually it should get to at least 15 to keep up with Weapon Master. I prefer two-hand weapons or pole-arms since he is disposable, and a few points in power throw.
The combination of Tactician and Engineer make Artimenner's primary attribute INT, while Engineer provides bonuses to crossbows based on Weapon Master (AGl) and improves his capacity as a Castle Steward based on his Engineer & Trade skills. Since you only need two of the six INT skills provided by pumping INT, consider making him a doctor or a scout, or leveling Trainer to add to the daily xp. He's probably best used either as a crossbowman, to protect the utility of his party skills & improve his crossbow skills before level 20, or as a medium-armored infantry unit, if you want to make us of his Shield Basher and Tactician abilities.
Lezalit is the best Captain of the Guard. His Siege General ability might not immediately seem powerful, as it does not display for you what it does during a siege, but it has no range limitation so every defending troop receives all of his powerful enhancements. Round CHA up to 9 for a third Leadership as you approach level 20, and post him in a key location. More generally, INT/Tactics are his main focus, but you may as well level his Engineer, Trainer, or scout/doctor skills with the spare skill points. Decent combat skills; can be used in any division, but best as medium infantry or as a crossbow commander.
Borscha works well as a medium-armored lancer, styled after Khergit lancers, with high Riding and Weapon Master skills; his Nimble ability helps him with encumbrance from medium armor. Scavenger grants more battlefield loot based on Looting, so prioritize that. Round STR up to 9 for a third Ironflesh. I round his INT and scout skills to 15/5, except Tracking, because Tracking isn't very useful. He can serve a party role later on with Useful Contacts (see Nizar), but due to mediocre Trade/Prisoner Management skills, he's not great at any of them.
Pure warrior. No skills to help with ENC, so manage weight wisely as she increases in STR. Pump STR, but keep AGI respectable to keep up with Weapon master. Give her the best two-hander you can find, and a pack full of javelins. Pump Ironflesh and note that she gains damage as she loses health.
Rolf is a warrior with a benefit to nearby troops via Commanding Presence. He could go Cavalry or Infantry. I prefer the latter, because Infantry tend to fight cohesively, whereas Cavalry lose cohesion after the first charge. Unlike Matheld, I like him to have a shield even though he is somewhat suited to two-handers, to keep him alive and make optimal use of his troop benefit. Focus on STR, but keep AGl respectable. Disregard CHA – put one extra point into Leadership then read a book to get to 4.
KLETHI Scavenger Poisoned Weapons Sharpshooter Pump AGI and looting for Klethi. Give her a crossbow and keep her with the foot archers. Her initial three in Power Throw is tempting, but disregard it as she is not a STR build.
JEREMUS Quick Study N/A Administrator Jeremus begins set up as a doctor. Put extra points into Training and Leadership in anticipation of his future capabilities as a steward. Crossbow, keep him back. No horse. No limit on armor.
YMIRA Inspiring Quick Study Administrator Ymira is still a blank slate character, but her Silverstag abilities don’t lend themselves to her being much of a fighter. Her role for me is a doctor of choice over Jeremus. Put a couple points into CHA and use books to round up to four Leadership for its morale bonus.
BUNDUK Prior to 0.26: Fortitude Boundless Endurance N/A Bunduk’s abilities lend themselves to any combat role, although light/medium Infantry benefits from them most. They are not driven by any attribute. He does not get any help with ENC, so manage his weight. I personally like him as a medium armored two-handed heavy hitter on foot. He brings no party skills to the table, so I don’t care if he gets knocked out.
After 0.26: Rapid Reload Boundless Endurance Firing Captain Bunduk loses fortitude, but gains a pair of skills that makes him more useful as a crossbowman or firearms user. If you have a lot of crossbow units, give him one as well and pump leadership. Otherwise, he still has his sprinting boost so consider keeping him as infantry.
DESHAVI Trailblazer Sharpshooter Master Archer I keep Deshavi around even under a morale penalty as passive boost to path-finding. She eventually comes into her own as a powerful archer on par with Nissa, but it takes her longer to get there. Kit her out as a light archer, focusing on AGI and Weapon Master.
Group Choices Nissa should be taken as she is not plugged into the “like/dislike” circles. As a reminder for an agreeable party, select one group from each circle [S1, S2; B1, B2], where: • S1 = Alayen, Firentis, Baheshtur • S2 = Nizar, Katrin, Marnid • B1 = Borcha, Artimenner, Matheld, Lezalit, Rolf • B2 = Klethi, Jeremus, Ymira, Bunduk, Deshavi
The royals are all of S1 (Alayen, Firentis, Baheshtur), plus three from B1 (Rolf, Lezalit, Matheld). All of the best party role companions are contained in S2, which I consider a must-have in Silverstag. Neither of the B groups contain any must-haves, but I gravitate toward B1 largely for aesthetics. I tack on Baheshtur for Hunting, and Deshavi for Trailblazing, and just suffer the disagreements. Baheshtur likes Rolf, although Deshavi likes nobody in my choice. She hasn’t bailed yet, but I won’t be sad if she does.